1. Field of the Invention
This invention relates to a process for the production of a surfactant-containing amorphous alkali metal silicate/alkali metal carbonate compound with multiple wash cycle performance which may be used as a water-soluble builder in detergents or cleaners, to the use of such alkali metal silicate compounds in detergents or cleaners, to extruded detergents or cleaners and to a process for their production.
Modern compacted detergents or cleaners generally have the disadvantage that, on account of their compact structure, they exhibit poorer dissolving behavior in aqueous liquors than, for example, lighter spray-dried detergents or cleaners of the prior art. Detergents or cleaners generally tend to dissolve more slowly in water, the higher their degree of compaction. Because they are insoluble in water, the zeolites normally present as builders in detergents or cleaners can additionally contribute towards the impaired dissolving behavior.
A water-soluble alternative to zeolites are amorphous alkali metal silicates with multiple wash cycle performance.
2. Discussion of Related Art
It is known that powder-form hydrated water-soluble silicates still containing about 20% by weight of water can be obtained by the spray drying or roll drying of waterglass solutions (cf. Ullmanns Enzyclopadie der technischen Chemie, 4th Edition 1982, Vol. 21, page 412). Products of this type are commercially available for various purposes. Corresponding powders have a very loose structure as a result of spray drying. Their bulk densities are generally well below 700 g/l.
Granular alkali metal silicates with relatively high bulk densities can be obtained in accordance with the teaching of European patent application EP-A-0 526 978. In this process, an alkali metal silicate solution with a solids content of 30 to 53% by weight is introduced into a heated drum in the longitudinal axis of which rotates a shaft with a plurality of arms reaching almost to the inner surface of the drum, the drum wall having a temperature of 150 to 200.degree. C. The drying process is supported by a gas introduced into the drum at a temperature of 175 to about 250.degree. C. This process gives a product with an average particle size of 0.2 to 2 mm. A preferred drying gas is heated air.
European patent application EP-A-0 542 131 describes a process in which a product completely soluble in water at room temperature with a bulk density of 500 to 1200 g/l is obtained. Heated air is preferably used as the drying gas. This process also uses a cylindrical dryer with a heated wall (160 to 200.degree. C.) in the longitudinal axis of which a rotor with blade-like vanes rotates at such a speed that a pseudoplastic paste with a free water content of 5 to 12% by weight is formed from the silicate solution with its solids content of 40 to 60% by weight. Drying is supported by a hot air stream (220 to 260.degree. C.).
Earlier hitherto unpublished patent application P 44 19 745.4 also describes a water-soluble, amorphous and granular alkali metal silicate which is produced by a process similar to that described in EP-A-0 526 978, but contains silica. The term "amorphous" in this context means "X-ray amorphous". This means that the alkali metal silicates do not produce any sharp reflexes in X-ray diffraction patterns, but at best one or more broad maxima of which the width amounts to several degrees of the diffraction angle. However, this does not mean that regions producing sharp electron diffraction reflexes cannot be found in electron diffraction experiments. This may be interpreted to mean that the substance contains microcrystalline regions up to about 20 nm (max. 50 nm) in size.
Granular amorphous sodium silicates obtained by spray drying of aqueous waterglass solutions and subsequent grinding, compaction and spheronizing with additional drying of the ground material are the subject of U.S. Pat. Nos. 3,912,649, 3,956,467, 3,838,193 and 3,879,527. The products obtained have water contents of about 18 to 20% by weight for bulk densities well above 500 g/l.
Other granular alkali metal silicates with multiple wash cycle performance are known from European patent applications EP-A-0 561 656 and EP-A-0 488 868. These documents relate to compounds of alkali metal silicates with certain Q distributions and alkali metal carbonates. The products are obtained by granulating powder-form water-free sodium carbonate in the presence of a sodium silicate solution (waterglass solution) and drying the products so that they have a certain residual water content bound to the silicate. According to tests conducted by applicants, products such as these have a relatively low absorption capacity for nonionic surfactants of &lt;30 g nonionic surfactants per 100 g of compound. It is not known from the prior art that compounds such as these can be produced using aqueous formulations of anionic surfactants.
Intentional patent application WO-A-91/02047 describes a process for the production of high-density extrudates in which a solid free-flowing compound is extruded under pressure in strand form. The solid free-flowing compound contains a plasticizer and/or lubricant which ensures that the compound softens and hence becomes extrudable under the pressure applied or under the effect of specific energy. After leaving the multiple-bore extrusion die, the system is not exposed to any further shearing so that its viscosity increases to such an extent that the extruded strand can be cut to predetermined extrudate dimensions. Now, it is known from International patent application WO-A-94/09111 that the compound to be extruded must contain both components which show pseudoplastic behavior and components which have dilatant properties. If the compound were only to contain components with pseudoplastic behavior, it would soften or even become almost liquid under the effect of the pronounced shear gradient to such an extent that, after leaving the multiple-bore die, the strand would no longer be cuttable. For this reason, dilatant components are also used, i.e. components which show increasing plasticity with increasing shear gradient and which thus guarantee the cuttability of the extruded strand. Most ingredients of detergents or cleaners show pseudoplastic behavior. Dilatant behavior is more the exception. However, there is one ingredient of conventional detergents or cleaners which does possess dilatant properties, namely the water-insoluble alumosilicates, such as zeolites, used as builders and phosphate substitutes. Although extruded detergents or cleaners containing 19% by weight of zeolite (based on water-free active substance), 12.5% by weight of sodium carbonate and 2.2% by weight of amorphous sodium silicate are known from International patent application WO-A-94/09111, it was not known that, in terms of process technology, zeolite could be partly or even completely replaced by water-soluble inorganic builders, such as amorphous alkali metal silicates, providing they are used in a certain form.
German patent application 195 01 269.0 describes amorphous alkali metal silicate compounds with multiple wash cycle performance and a molar ratio of M.sub.2 O to SiO.sub.2 (M=alkali metal) of 1:1.5 to 1:3.3 which contain anionic surfactants, preferably alkyl benzenesulfonates and/or alk(en)yl sulfates. In one preferred embodiment, these compounds additionally contain 30 to 70% by weight of alkali metal carbonate. They are produced by spray drying of an aqueous slurry containing all the ingredients of the alkali metal silicate compound.
EP-A-651 050 describes a process for the production of granules which contain as essential components an amorphous silicate, an anionic surfactant and another solid salt, for example sodium carbonate. This additional salt is initially introduced and is agglomerated with an aqueous "binder" of alkali metal silicate solution and anionic surfactant. Sodium carbonate is one of many suitable salt components. Whereas the binder contains the alkali metal silicate and the anionic surfactant in ratios by weight of 1:3 to 3:1, there is no mention whatever of the ratio by weight between "binder" and salt component. The agglomerates produced in accordance with the Examples have sodium carbonate contents below 10% by weight. The preferred salt present in quantities of 35.5% by weight in the Examples is sodium sulfate.
One of the problems addressed by the present invention was to provide further water-soluble builders for the partial or complete replacement of zeolite in detergents or cleaners so that the dissolving behavior of heavy detergents or cleaners in particular would be improved. In addition, these water-soluble builders would also have an absorption capacity for ingredients of detergents or cleaners which are liquid to wax-like at the processing temperature. Another problem addressed by the present invention was to provide extruded detergents or cleaners which would contain the water-soluble builders in such quantities that zeolite could be completely or partly replaced not only in performance terms, but also in terms of process technology, and a process for their production.